1. Field of the Invention
The invention relates to a high-definition multimedia interface (HDMI) technique, and more particularly to an HDMI receiver apparatus, a method for controlling a hot plug detection signal, and an HDMI system.
2. Description of the Related Art
A high-definition multimedia interface (HDMI) is a digital video/audio interface technique which has extensive applications. For HDMI circuits, the conventional design adopts an external electrically erasable programmable read-only memory (EEPROM) for storing extended display identification data (EDID) and uses two general-purpose I/O ports (GPIOs) for respectively performing HDMI cable detection and hot plug detection, thereby controlling the HDMI system. Specifically, when a transmitter (a TX terminal, also called a source terminal) of an HDMI system is connected to a receiver (an RX terminal, also called a sink terminal), the receiver sends a hot plug detection signal to the transmitter. Then the transmitter activates a display data channel (DDC) to read EDID information from the receiver and performs a high-bandwidth digital content protection (HDCP) handshake to achieve mutual authentication. When the mutual authentication is successful, video and audio operations are performed normally; otherwise, the connection fails.
In recent years, with a need for reduction in peripheral integrated circuits (ICs) and simplification of circuit design, the external EEPROM has been replaced with EDID embedded in a system on a chip (SOC). When the embedded EDID is adopted, hot plug detection is usually achieved in the following manner. FIG. 1 shows a schematic view showing a conventional detection circuit for an HDMI receiver. As shown in FIG. 1, when there is embedded EDID, the HDMI receiver uses two general-purpose I/O pins (pins GPIO1 and GPIO2 shown in FIG. 1) to accomplish HDMI control, wherein the pin GPIO1 is used to detect whether an HDMI cable is connected to the HDMI receiver, and the pin GPIO2 is used to control a hot plug detection output level. Specifically, when an HDMI cable is connected to the HDMI receiver, the HDMI receiver would detect a high-level signal on the pin GPIO1. Then the HDMI receiver outputs a low-level hot plug detection signal to an HDMI transmitter through the pin GPIO2, wherein the low-level hot plug detection signal has a length of at least 100 ms. Subsequently, the HDMI receiver changes the low-level hot plug detection signal at the pin GPIO2 to a high-level hot plug detection signal. When the HDMI transmitter detects that the level of the hot plug detection signal has been changed, the HDMI transmitter starts reading the EDID and transmits an HDMI signal. The described high-level hot plug detection signal may be at a level ranging from 2.4V to 5.3V.
When the above manner is adopted to achieve the control of the hot plug detection signal in the receiver with the embedded EDID, two I/O pins are required, which is disadvantageous to high-density integration of HDMI systems.